Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications.
Natural gas, when used in a mobile application, is generally stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, typically below about −150° C. The liquefied natural gas is then drawn from the tank by a charge pump and directed via separate passages to individual plungers of a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine's engine. In some applications, the liquid fuel is gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.
One problem associated with conventional high-pressure pumps involves large temperature differences that can cause thermal distortion and stress challenges in components of the pump. Specifically, the pumps often have bolted joints, which can be subject to thermal expansion. This thermal expansion, if not accounted for, can cause failure of the joint.
One attempt to improve longevity of a cryogenic pump is disclosed in U.S. Pat. No. 5,860,798 (the '798 patent) that issued to Tschopp on Jan. 19, 1999. In particular, the '798 patent discloses a pump having a piston that reciprocates within a bush to propel a cryogenic fluid. A sleeve-like bearer defines an inlet for the pump and houses the bush with an Intermediate space in between. In operation, a portion of the cryogenic fluid is diverted from the inlet into the intermediate space to thermally insulate the bush. This feature is intended to ensure a steady stream of cryogenic fluid by preventing gas bubbles or warm fluid inside the bush.
While the pump of the '798 patent may inhibit heat transfer within the pump and thereby increase longevity of the pump, it may still be less than optimal, in particular, the '798 patent has a simple design limited to a single piston. Further, the design focuses on insulation of the cryogenic fluid and does not take into account the components (e.g. bolted joints) of the pump.
The disclosed pump is directed to overcoming one or more of the problems set forth above.